The role of brittle fracture in determining sea ice floe size distribution

There have been several recent efforts to develop parameterisations of the sea ice floe size distribution (FSD) for use in sea ice models such as CICE and SI3. These models aim to capture the key processes that determine the evolution of floe sizes, including melting at the edges of floes, welding together of floes, and break-up of floes by waves. However, several fragmentation processes are not yet accounted for in these models. For example, in-plane brittle fracture events can have a direct impact on the size of larger floes and potentially also smaller floes. Plausible indirect mechanisms also exist. It has been observed that thermodynamic weakening of cracks and other linear features in the sea ice cover can in some cases drive the break-up of sea ice in the central Arctic. These observations imply that linear features in the sea ice that form in winter from in-plane brittle fracture before freezing up can then determine the fragmentation of sea ice in summer as it thins and weakens. 

Here we will present results from sea ice simulations including a prognostic model of sea ice FSD to show that the inclusion of brittle fracture-derived impacts on floe size improves the performance of the FSD model in simulating observed FSD shape for mid-sized floes. We will use these results to motivate the development of a more physically derived parameterisation of floe breakup via thermal weakening of floes along existing linear features. Finally, we will discuss how we can combine novel observations and recent advancements in modelling techniques such as discrete element methods applied to sea ice to aid in the development of parameterisations of these floe-scale processes for subsequent application in continuum models.